The present invention relates to (partly) bio-based copolyesters suitable for use in latex compositions, a process for preparing such copolyesters by a copolymerization of a first diol being an isohexide, a cyclic dicarboxylic acid and a (second) diol. The present invention further relates to a latex composition comprising said copolyester and a process for preparing such a latex. The invention also relates to inkjet inks comprising said polyester latex.
A latex is stable dispersion of polymer nano- or microparticles in a liquid, preferably water.
State of the art latex-inks comprise a resin which constitutes the main solid fraction of the ink, and colorant(s) dispersed in water. For tuning ink properties additives such as co-solvents and/or dispersing agents may be used. Commonly used resins in latex-inks are petrochemically based synthetic polyesters and/or polyacrylics.
In general, the used polyesters are synthesized using phthalates and/or bisphenol A as monomers. Such monomers more and more become a point of discussion in relation to health issues. Moreover, increasing oil-prices may render petrochemically based (polymeric) materials too expensive and therefore not feasible for a number of applications, in particular when used in products having a short life-time. Therefore there exists an increasing need for other resources of starting materials for polymeric materials (in this case in particular polyesters) having no health issues or at least to a lesser extent and preferably being cheap.
The application of such polymers in ‘short-life’ or disposable products, for example in inks for printing transient documents (e.g. newspapers, magazines, personalized mail, advertising materials and the like) also requires that the polymers are biodegradable. Inks comprising polymers having an improved biodegradability may show better de-inkability, because the ink components will decompose more easily and detach from the paper fibers in the recycle process. With an improved de-inkability, the quality of the recycled paper may increase.
Isohexides (i.e. isosorbide, isomannide and isoidide) have been identified as an interesting source of renewable raw materials for many applications. Isohexides are readily made from renewable resources such as sugars and starches. For example, isosorbide (also referred to as D-isosorbide) can be made from D-glucose by hydrogenation followed by acid-catalyzed dehydration. Polymers comprising isohexides as monomers (bio-esters) are known for their biodegradability.
U.S. Pat. No. 6,485,819 B2 discloses a copolyester of the reaction product of: (a) one or more aromatic dicarboxylic acids or an ester thereof; (b) one or more aliphatic dicarboxylic acids or an ester thereof; and (c) isosorbide. U.S. Pat. No. 6,485,819 also discloses that such polyesters are useful to form articles of increased biodegradability.
U.S. Pat. No. 6,762,276 discloses a process for hydrogenating a polyester oligomer containing terephtalic acid residues wherein terephtalic acid residues are converted to residues of 1,4-cyclohexanedicarboxylic acid. Further disclosed is a process for polymerizing the hydrogenated polyester oligomer.
U.S. Pat. No. 4,418,174 discloses dianhydromannitol (isomannide), dianhydrosorbitol (isosorbide) and dianhydromannitol semi-esters and dianhydrosorbitol semi-esters to be outstanding raw materials for the production of aqueous stoving lacquers based on polyesters. The disclosed aqueous stoving lacquers are compositions comprising (A) from 10 to 90% by weight of polyester having an average molecular weight Mn of from 1000 to 10000; (B) from 10 to 50% by weight of a reactive diluent, which are understood to be low-viscosity materials which dilute resinous binders and thus impart to the lacquer the viscosity which is required for its application, which contain functional groups capable of mixed polymerization of mixed condensation with the lacquer resin (A), and which, during the hardening procedure (i.e. curing), mainly become a component of the hardened lacquer film. The reactive diluent therefore also acts as a crosslinking agent; (C) up to 50% by weight of water; and (D) from 0 to 40% by weight of an aminoplast resin. The percentages are based on the sum of components A, B and D.
(Co)polyesters and (co)polyester compositions known from the prior art are not optimized for use in a latex, or in particular in a latex ink. For being suitable to be used in a latex ink a resin has to fulfill a number of specifications demanding possibly conflicting material characteristics. For example for a latex ink a (binder) resin is needed which is not too brittle to obtain good scratchfastness of the print. This translates into the property of polymer in the latex having a glass transition temperature (Tg) not too far removed from the temperature of use of the print, usually ambient temperature. On the other hand for anti-blocking demands (i.e. unwanted transfer of ink from a print to another substrate under pressure and heat) of the print it is important that the binder material has a high enough softening point, i.e. Tg. Both requirements being in conflict with each other.
For anti-blocking properties and waterfastness of the print, the resin also needs to be waterresistant, i.e. water repellent, which translates into hydrophopicity of the printed ink.
For the purpose of the present invention an ink is sought that is jettable, i.e. an ink suitable for use in an inkjet process.
It is therefore an object of the present invention to provide (partly) bio-based polyesters suitable for use in a latex, in particular in latex inks, having satisfactory anti-blocking properties, waterfastness and jettability.
It is another object of the present invention to provide a method for preparing such (partly) bio-based copolyesters.
It is another object of the present invention to provide a process for preparing a latex composition of (partly) bio-based polyesters.
It is yet another object of the present invention to provide a latex, in particular a latex ink comprising a (partly) bio-based polyester binder having such properties that the above stated requirements are at least partly satisfied.